Skeletal Cartilages: structures, types & locations
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Skeletal cartilage –
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Made from cartilage
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Consists primarily of water
Allows for resilience
No nerves or blood vessels
Surrounded by a layer of dense irregular connective tissue – perichondrium
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Resists outward expansion when compressed
Source of blood vessels – feeds the matrix & chondrocytes
Hyaline cartilage –
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Hyaline cartilage is the most abundant skeletal cartilage, and includes the articular (cover bone ends @ movable joints), costal
(connects ribs to sternum), respiratory (larynx & reinforce passageways), and nasal (external nose) cartilages.
Provide support & flexibility (due to collagen fibers)

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Elastic cartilage –
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More flexible than hyaline
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Contains more elastic fibers
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Located in the external ear & epiglottis
Fibrocartilage –
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Located in areas that need to withstand a great deal of pressure & stretch
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Chondrocytes & collagen fibers
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Knee & intervertebral discs

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Appositional –
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“growth from the outside”
Outward expansion due to production of cartilage matrix on the outside of tissue
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Secrete new matrix against the external surface of the existing cartilage
Occurs in the shafts of long bones
Interstitial –
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“growth from the inside”
Expansion within the cartilage matrix due to divisions of lacunae-bound chondrocytes & secretions of the matrix
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Occurs in the ends of bone

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206 bones in the body
2 divisions –
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Axial –
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Consists of:
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The skull, vertebral column, & rib cage
Involved in protection, support, or carrying other body parts
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Appendicular –
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Consists of:
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The bones of the upper & lower limbs & the girdles
(shoulder & hip bones) that attach them to the axial skeleton

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Long bones –
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Longer than they are wide
Have a definite shaft & two ends
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Consist of all limb bones except:
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Patellas, carpals, & tarsals
Named for their shape not size (fingers are long bones even though they are small)
Short bones –
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Somewhat cube-shaped
Include –
 the carpals & tarsals
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Sesamoid – bones that form with in tendons (patella)

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Flat bones –
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Thin, flattened, and often curved bones
Include –
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Skull bones, sternum, scapulae, and ribs
Irregular bones –
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Complicated shapes
Don’t fit into any other class
Include –
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Vertebrae
Hip bones & coxae

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5 main functions –
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Support –
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Support body
Cradle soft organs
Protection –
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Protect vital organs
Movement –
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Allow movement
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Muscles attach to bones acting as levers for movement
Mineral storage –
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Store calcium & phosphate
Released into the blood stream as ions for distribution to the body
Blood cell formation –
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House hematopoietic tissue

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Bone markings –
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Projections;
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Muscle attach to and pull
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Modified for where bones meet (joints)
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E.g. heads, trochanters, spines
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Depressions and openings;
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Allows passages of nerves and blood vessels
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E.g. fossae, sinuses, foramina, grooves
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Table 6.1 pg. 179

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External layer = compact bone
Internal layer = spongy bone
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Made of trabeculae

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Diaphysis –
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The bone shaft
Contains cavity with yellow marrow
Epiphysis –
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Ends of long bones
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Typically wider than diaphysis (shaft)
Consist of internal spongy bone & outer layer of compact bone
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Ends are covered with hyaline (protects bone ends where they meet at the joint)
Epiphyseal line/plate –
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Between epiphysis & diaphysis
Line = remnant of plate (hyaline cartilage disc in young adults that lengthens bone)

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The external surface of bone is covered by the periosteum
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Double layered membrane
Covers all bones except joint surfaces
Contains osteoblasts & osteoclasts
Richly supplied w/ blood, nerve fibers, & lymphatic vessels – enter bone shaft via nutrient foramen
Secured to bone shaft by – Sharpey’s fibers – tufts of collagen fibers
Provides insertion points for tendons and ligaments
The internal surface of bone is lined by a connective tissue membrane called the endosteum
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Covers trabeculae of spongy bone
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Lines canals that run through compact bone
Also contains osteoblasts & osteoclasts

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Short, flat, & irregular bones consist of thin plates of periosteum-covering compact bone on the outside, and endosteum-covered spongy bone inside, which houses bone marrow between the trabeculae
No shaft or epiphyses
Flat bones – internal layer of spongy bone = diploë

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Hematopoietic tissue = red bone marrow
Located within trabecular cavities of the spongy bone, in diploë of flat bones & epiphysis of long bones
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Infants – all areas of spongy bone contain red marrow
Adults – epiphysis of long bones – diaphysis – yellow marrow

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2 types of bone texture –
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Compact –
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Appears dense, smooth & solid
Contains passageways for blood vessels & nerves
Osteon –
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 structural unit of bones tiny weight bearing pillars arranged like tree rings
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Each matrix tube = lamella
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Collagen fibers run in same direction – in opposing lamella they run in opposing directions – allow extra strength
Haversian canal –
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Center of osteon
Contain blood vessels & nerves
Lacunae –
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Contain osteocytes – mature bone cells
Canaliculi – connect lacunae to each other and the central canals
Interstitial lamellae –
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Incomplete lamellae between osteons
Circumferential lamellae –
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Deep to the periosteum
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Superficial to endosteum
Resist twisting of long bones

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Compact bone – dense and solid
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Structural unit = osteon
Contains lamellae, Haversian canal, & blood vessels and nerves
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Volkmann’s canals –
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Lie at right angles to the long bone axis
Connect blood & nerve supplies of the periosteum to the central canals & medullary cavity
Osteocytes –
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Occupy lacunae & lamella junctions
Connected by canaliculi
Lamellae –
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Circumferential –
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Beneath periosteum
Interstitial –
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Between osteons

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Spongy –
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Internal to compact bone
Honeycomb, needle-like, flat pieces = trabeculae
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Align along the lines of stress
Help the bone to resist stress
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Contain irregularly arranged lamellae & osteocytes connected by canaliculi
No osteons present
Nutrients – diffused from canaliculi from capillaries in the endosteum

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Organic components
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Cells (osteogenic cells, osteoblasts, osteocytes, and osteoclasts)
Osteoid – ground substance and collagen fibers
Contribute to bone’s structure and flexibility
Inorganic components
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65% mineral salts (calcium phosphates)
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Tightly packed crystals around collagen fibers
Contribute to bone’s hardness – resists compression

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Ossification or osteogenesis = process of bone formation
Before week 8, skeleton made up of fibrous membranes and hyaline cartilage
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Flexible and resilient, can accommodate mitosis
Intramembranous ossification –
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Formation of cranial bones of the skull and clavicles
Endochondral ossification –
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All bones below base of the skull (except clavicles)
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Hyaline cartilage broken down as ossification proceeds

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During youth bones lengthen entirely by interstitial growth from the epiphyseal plates
Growth in length –
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The cartilage cells at the top of the epiphyseal plate
(closest to the epiphysis) push the epiphysis away from the diaphysis causing the bone to grow
Old chondrocytes (closer to the diaphysis) calcify & replace the cartilage with bone tissue
Growth in width –
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Occurs through appositional growth
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Bone growth due to deposition of bone matrix by osteoblasts beneath the periosteum

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Hormonal regulation
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Infancy and childhood – growth hormone stimulates epiphyseal plate activity
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Released by anterior pituitary gland
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Thyroid hormones regulate the activity of growth hormone ensuring proper bone proportions
Testosterone and estrogens are released in increasing amounts at puberty
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Initially – growth spurt, later induce epiphyseal plate closure

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Bone remodeling –
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Weekly recycle 5-7% of bone mass
Spongy bone replaced every 3-4 yrs
Compact bone replaced every 10 yrs
Adults –
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Balanced due to deposit & removal
Bone deposit occurs at a greater rate when bone is injured
Bone resorption allows minerals to be absorbed into the blood
Vit C (collagen synthesis), Vit D (absorption of dietary calcium), Vit A
(needed for balance between deposit & removal of bone)
Bone Modeling & Remodeling
Control of bone remodeling –
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Hormones – maintain blood calcium homeostasis
Mechanical stress & gravity – affect bone growth & allow bone to withstand stresses

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Response to mechanical stress
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Wolff’s Law : a bone grows or remodels in response to the demands placed on it
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Long bones are thickest midway along the diaphysis
(where bending stresses are greatest)
Curved bones are thickest where they are most likely to buckle
Trabeculae of spongy bone form trusses or struts along lines of compression
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Large, bony projections occur where heavy, active muscles attach

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Classification of fractures –
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Position of bone ends after fracture
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Nondisplaced fractures = bone ends retain normal position
Displaced fracture = bone ends out of normal alignment
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Completeness of break
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Complete fracture = bone broken through
Incomplete = not broken all the way through
Orientation of break relative to the long axis of bone
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Linear = parallels the long axis
Transverse = perpendicular to the bones long axis
Whether the bone ends penetrate the skin
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Open/compound = bone ends penetrate the skin
Closed/simple = bone ends don’t penetrate the skin

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Fractures are treated by reduction –
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Closed (external) reduction
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Bone ends coaxed into position by physician’s hands
Open (internal) reduction
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Bone ends secured together surgically with pins or wires
Check out Fig 6.2 on pg. 192 for other types
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Comminuted – common in elderly (brittle bones)
Compression – common in porous bones
Spiral – common sports fracture
Epiphyseal
Depressed – typical skull fracture
Greenstick – common in children (more organic matter)

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4 stages of fracture repair –
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1. Hematoma formation –
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Blood vessels are torn during the break, blood clot forms
Nearby bone cells deprived of nutrition and die
2. Fibroncartilaginous callus formation –
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Vessels begin to form
Phagocytic cells clean up debris
Fibroblasts (produce collagen fibers that reconnect the bone) & osteoblasts (begin forming spongy bone) begin to reform the bone
3. Bony callus formation –
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Bone trabeculae convert callus into bone
Begins 3-4 weeks after injury
Continues for about 2-3 months
4. Remodeling of bony callus –
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Excess material removed
Compact bone is laid down

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Osteomalacia & Rickets (in children)
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Bones inadequately mineralized
Caused by insufficient calcium or vitamin D deficiency
Osteoporosis
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Bone resorption outpaces bone deposit, bone mass reduced
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Spongy bone of spine most vulnerable and neck of femur (“broken hip”)
Caucasian women most susceptible group
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Estrogen helps restrain osteoclast activity
GET ENOUGH CALCIUM WHILE BONES STILL INCREASING IN
DENSITY! (Also, drink fluoridated water)
Paget’s Disease
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Excessive and haphazard bone deposit and resorption
High ratio of spongy to compact -> spotty weakening